The PI proposes to develop a focal infectivity assay (FIA) to quantify infectivity of HIV-1 primary clinical isolates, including macrophage-tropic viruses. The utility of the assay is to measure infectious virus present in a sample, and susceptibility to neutralizing antibody or to antiviral drugs. The long-term goal of this assay is to allow physicians to use the best antiviral drugs or combination of drugs for individual patient's needs. The FIA assay is limited to T cell-tropic HIV and has been carried out in Hela cells expressing CD4. In this feasibility study the investigators propose to extend this knowledge to macrophage-tropic HIV by transfecting CD4+ Hela cell with CCR5 which is the HIV-1 fusion accessory molecule for macrophage-tropic primary HIV-1 isolates. The expression of CCR5 in the cells and the degree to susceptibility to infection with macrophage-tropic HIV will be tested as well as the utility of the assay in measuring drug resistance and antibody-mediated neutralization.